Method and system for producing a plurality of images of the same object from the same point of view at the same time



Drasman June 10, 1924.

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D. F. COMSTOCK. IETHOD AND SYSTEM FOR PRODUCIHG A PLURA OBJECT FROM THESAIE POINT OF VI Filed Feb. 9,

2 Sheets-Sheet 2 uar'mnfvunennnY Patented June l0, 1924.

UNITED STATES PATENT OFFICE.

DANIEL F. COMSTOCK. OF BROOKLINEy MASSACHUSETTS. ASSIGNOR. BY MESNE AS-SIGNMENTS. TO TECHNICOLOR MOTION PICTURE CORPORATION, OF BOSTON, MASSA-CHUSETTS, A CORPORATION OF MAINE.

METHOD AND SYSTEM FOR PRODUCING A PLURALITY OF IMAGES OF THE SAME OBJECTFROM THE SAME POINT OF VIEW AT THE SAME TIME.

Application filed February 9, 1916. Serial No. 77,237.

To all viv/10m t may concern Be it known I. DANIEL F. CoMsTooK, acitizen of the United States, and resident of Brookline. in the countyof Norfolk and State of Massachusetts. have invented new and usefulImprovements in Methods and Systems for Producing a Plurality of Imagesof the Same Object from the Same Point of View at the Same Time, ofwhich the following is a specification.

In colored motion-picture projection it has heretofore been thecommercial practice to project successively through color-screens Iilmpictures taken successively through color-screens. The results obtainedby this method have been open to two serious objections: first, thedisplacements in successive pictures of the moving objects cause thoseparts of the moving objects which do not coincide in the successivepictures to appear in the colors of the several color screens ratherthan in the natural colors which would result from the blending orfusion of the several colors: second, the eye is fatigued by thealternate bombardment of light of different colors. The first difficultycauses what are called fringes and is especially bad when rapidly movingobjects are photograplied. The second difficulty causes a feeling of eyestrain which is distinctly objectionable.

To overcome this it is desirable to project simultaneously throughdifferent colorscreens two or more photographs, taken throughcolor-screens, of the same scene from accurately the same point ofviewat the same time. This involves the problem of obtaining on a film orfilms two or more photographs from accurately the same point of view, ofthe same scene at the same time.

The problem admits of solution along several distinct lines, accordingas one or more lenses are used in the camera, and according as thesinmltaneous photographs on the film are similarly arranged. or aresymmetrical with relation to a common axis, but inverted or reversedwith relation to each other.

In the accompanying drawings, Figs. 1 to l1 inclusive illustratediagrammatically several possible optical systems for obtaining, in acamera, a plurality of photographs of the. same scene from accuratelythe same point of view at the same time, disregarding certainrefinements which need not be considered in an explanation of thefundamental optical principles involved; and Figs. 12 and 13 illustratecertain symmetrical arrangements on the film of the relatively invertedpictures produced by the system in certain of its forms.

Referring to Fig. 1, O represents the object the scene to bephotographed), L represents the lens, and F represents the film. Thelight beam B from the object passes through the lens and the glass prismP, perpendicular to surface .r of prism P, to the semitransparentreflecting surface fc, which may be made by half-silvering the surfaceof prism P, or by introducing between P and P a film of some transparentsubstance of suitable refractive index, or which may be a light dividinggrid of transparent material having distributed thereon distinct areasof transmission and of reflection made according to my application,Serial No. 54.270. filed October 5. 1915. Essentially one-half of thelight is reflected from surface a: along the path B to the totallyreflecting surface .132. and thence along path B to thel film, formingan image on the film F at M. `The remainder of the light passes throughvsurface ai and through prisms` P and P to the totally reflectingsurface y, paralled to a?, of the prism P', and is thence refiectedalong the path B2 to the totally reflecting surface y', parallel to :02,of prism P,` and thence along path B22 to the film, and forms a secondimage on the film F at N. Prism P is separated from prisms P and P by athin film of air or other substanceofWO sufficiently low refractiveindex to insure total reflection from surface y. This4 system givesimages similarly' arranged, that is, head to foot, since each beam isreflected twice. By the inclusion of prism P" the geometrical lengths oftwo paths of the divided beam in the same or similar media are the same.

Fig. 3 shows the same principle applied to the formation of threesimultaneous pictures similarly arranged (he-ad to foot), and scarcelyneeds additional explanation. The

beam B enters prism P through surface x2, which is normal to the. beam.Partly transparent reflecting surface .r reflects essentially one-thirdof the light along path B', to the totally reflecting surface fr andthence along path B to the film F. forming an image at M. The remainderof the light passes t-hrough prism PIv to semi-transparent reflectingsurface y, where the beam is again split, substantially half being re`flected along path B2 to the totally reflecting surface y and thencealong path B22 to form the image N on the film, while the remainder ofthe beam passes through prism P, (which furnishes a medium of glass) andprism Pv to totally reflecting surface s. thence along path B3 tototally reflecting surface a', and thence to the film forming an imageat O. The surfaces y and s are totally reflecting surfaces, the lattertwo being rende-red so by films of air between said surfaces and theadjacent prisms. or by applying to the surfaces y and a of prisms Pi"and Pv some medium of suitable refractive indeX such as ordinary balsam,which has a sufficiently low index of refraction to yield totalreflection, as in the case of air, and also affords protection againstthe soiling of the glass surfaces. The prisms P" and Plv-are hollowedout opposite surfaces y and a', and are coated with black balsam asshown at k, c, or other suitable material, to prevent any stray light.from passing between the prisms P" and Pv, and prisms Piv and P". For ain particular it is desirable to use a film of only slightly lower indexthan the glass. which, without interfering with the total reflection ofray B3, will diminish the loss by reflection of part of the initial beamB when entering the prism P".

Referring now to Fig. 2, which illustrates another form, O representsthe object, L the lens, and F the film, as before. The light beam Bpasses through the lens and the glass prism P2 to the semitransparentreflecting surface whe-nce one-half the light is reflected to thetotally reflecting surface m2, and thence out of theprism to the film,forming the image at M. The remainder of the light passes on through thesurface and the prism P3 to the totally reflecting surface y2, andthence out of the prism to the film. forming a second image at N,inverted with relation to the image M, (one beam having been reflectedtwice and the other once), so that the pictures on the' film appear headto head or foot to foot.

It is desirable that prisms P2 and P3 be right-angled and identical, inorder that the optical paths to the two images may be equal. It is alsodesirable, though not essential, that they form in section anequilateral triangle,in other words, that the angles 1, 2, and 3 be each60, s0 that @he beam enters normally to the surface. If for any reasonit is desired to use other angles a thin auxiliary prism may beinterposed. presenting one face normally to the incident light, andhaving the other separated by an airfilm from surface .n2 of prism P2.This avoids the dispersion due to Obliquity: but no advantages areobtained by departing from the form.

The distinctive feature to be observed in the form shown in Fig. 2 isthe complete geometrical symmetry of the two beams and images withrespect to the semitransparent surface .11 after leaving it. Suchsurface may thereforeI be termed the symmetrical plane.

It is evident that much space is saved by using the surface r2 of theprism P2 both as a transmitting surface, when the light first enters theprism, and also as a totally reflecting surface for that part of thelight reflected back by surface fc.

Instead of placing the symmetrical plane behind the lens, that is,between the lens and film, in which case the beam first passes throughthe lens and is then split to form two images, it may be placed beforetwo or more lenses, that is, between the object and the lenses` as shownin Fig. 4, in which casethe beam B is first split at the semitransparentsurface ,r and then the two parts pass through two lenses L and L2 tothe two images M and N on the film. This arrangement makes the point ofview of the two lenses the same, and avoids the stereoscopic effectwhich would result if'the light passed directly from the object to thetwo lenses in two distinct beams. Since one beam has undergone one morereflection than the other, the images will be relatively inverted.

If it is desired to have the pictures similarly arranged. instead ofrelatively inverted, this may be accomplished by rotating one of theimages by reflection in a rightangled prism, as shown in 'Figs 5 and 6.This arrangement is identical with Fig. 4, with the addition of theplane reflector R and reversing reflector S. The beam passing throughlens L2 is reflected up at right angles to the plane of Fig. 5 by the 45plane totally reflecting mirror or similar reflector R; while the otherbeam passing through lens L1 is also reflected up at right angles to theplane of the drawing` but is reflected by means of a leaves-of-a-bookreflector S comprising two plane reflecting surfaces at right angles toeach other, which also reverses the image. or rotates it through 180.The reflectors R and S might obviously be a totally reflecting prism anda right angle prism, but for simplicity and clearness in drawing theyare shown as composed of plane mirror surfaces. The resultant images aretherefore similarly arranged instead lili of relatively inverted. Fig. 6shows Fig. 5 viewed from below. This inverting of one image is obviouslypossible with any symmetrical plane method.

Thus. in order to obtain two pictures from accurately the same point ofview at the same time. a symmetrical plane may he used. consisting of asemitransparent surface placed in a position either behind the lens andessentially symmetrical with respect to the two images, or in a positionin front of two lenses and essentially symmetrical with respect to them.The arrangement may be varied in several ways. but the essentialcondition in obtaining relatively inverted images isq the presence ofsuch symmetrical plane.

lVith the use of the .symmetrical plane it is possible to get. in thecase of one lens. two paths between the lens and the film. ofessentially the same lengths: and in the case of two lenses in the twopaths from the symmetrical plane to the film. the two lenses haveprecisely the same viewpoint regarding the scene to be photographed. Ineither case the two paths of the split light beyond the symmetricalplane where the light is split. are completely symmetrical to each otherand to the symmetrical plane.

With the use of' the' symmetrical plane systems above described. twoidentical` or inverted and symmetrical images may be ohtained on thefilm at the same time from precisely the same viewpoint. Such a filmwith relatively inverted or foot-to-f'oot pictures is illustrated inFig. 12. wherein F represents a film of usual form, and F and F a pairof foot-to-foot, simultaneously made pictures of the same scene.

Should it be desired to obtain more than two such pictures. sav three orfour. this can be accomplished by adding a second symmetrical planesystem to the system, illustrated in Fig. 2. in the manner presently tobe described. This will produce a. film with four pictures ot' the samescene (or three by merely7 dropping out one picture) taken at the sametime, from accurately the same point of view, and arranged symmetricallywith relation to two axes. one transverse and one longitudinal of thefilm. as illustrated in Fig. 13. In this form each picture F on the filmF is symmetrically arranged and invertedwith relation to the adjoiningpicture of the pair. whether considered lengthwise or crosswise of thefilm: and the four pictures are symmetrical and relatively inverted withrelation to two axes.

To produce such a film as that shown in Fig. 13, having four pictures ofthe same scene from the same point of view taken at the same time, thesystem illustrated in Figs. 7 and 8 may be used, Fig. 8 being anelevation viewed from the right of Fig. 7 The upper part A representsthe same system as Fig. 2. and will produce two images as alreadyexplained. ln order to get four pictures in symmetrical positionsanother similar set of prisms. twice as wide. is placed at B in suchposition that each ray is split again in a direction at right angles tothe former split produced by A. .Each of the two. split beams from A isagain split by the semit-ransparent reflecting surface m4, betweenprisms P and F5 ('Fig. 7) in the same manner as already described withreference toFig. 2. resulting in four symmetrical. relatively invertedimages as shown in Fig. 13.

It is further contemplated that the relatively inverted images producedby the symmetrical plane system may be images in register on oppositesides of the same film. An optical system employing for this purpose mysymmetrical plane method is shown in Fig. li. The upper part ot' thesystem, including prisms P2 and P3, is precisely the same as in Fig. 2.The split beams a and a refiected from surfaces .r2 and L1/2 enter thetwo right angle totally reflecting prisms P6 and P7, respectively, andare by them reflected normally inwardly toward each other alongsymmetrical paths to opposite sides of the film F, which passes througha narrow space between prisms P5 and P7. The images thus formed onopposite sides of the film will necessarily be in register. since theywere made foot-to-foot images by prisms P2 and P3. and the effect ofprisms i?6 and PT is to fold the two relatively inverted images uponeach other on a central axis. A special film sensitized on both sides.with the sensitive surfaces separated by a film or layer of opaquematerial, subsequently to be removed. as by dissolution. would be usedwith this system. Also to make the film of practical use in colorprojection the two sides of the film and the film itself would be dyedor otherwise colored. Such film, however, will not be further consideredas it forms no part of the invention herein claimed: the presentapplication is concerned with the optical system for forming the imagesrather than with the film.

Figs. 9 and l0 show perspective and plan views. respectively. of anotherarrangement of prisms for producing a result similar to that of thesystem shown in Fig. 3, namely, the formation on the same lm of threepictures simultaneously from accurately the same point of view, at equaloptic-al paths from the lens. This arrangement involves a longer opticalpaththan that of Fig. 3, one advantage over the latter being that itinvolves no angles other than 90 and 45 angles, thus requiring onlystandard shapes of prisms.

Both Figs. 9 and 10 are diagrammatic or schematic, and the oblique Viewof the system, shown in Fig. 9 as an aid to visualization. is a viewfrom an angle of approximately 45 to the plane of Fig. 10, from thelower left-hand corner. And in both figures no account is taken of therefraction of light due to entering and leaving the prisms at anglesother than right angles: in other words for the sake of clearness and toavoid complication in drawing, diagrams show the paths of the beams asthough the prisms wei'e leaves-of-a-hook-mirrors. The beam B is to bedivided into three parts, and for clearness is shown in three lines.From the lens L the beam falls upon the partly transparentreflectingsurface c, which may be any suitable form of light-dividingmeans such as a partly silvered surface. or a light-dividing grid,adapted to transmit substantially twothirds of the light and to reflectsubstantially one-third of the light, said surface c being arranged atan angle of 4.50 to the path of the beam. The reflected part of the beampasses along path b to the totally reflecting right-angle prism C, whoseapex C is in a plane below and parallel to the horizontal plane of thelight beam, and in a vertical plane at an angle of 45 to the split beamThe beam b strikes the upper face C2 of the prisms and is reflecteddownward along path b to the lower face C3, and thence along pat-h b2 tothe film F, forming an ima e at M. Said lower right-angle prism thusshifts the beam sidewise with relation to the prism, that is, lengthwiseof the film, and reverses the image.

The rest of the beam B passes along the path b3 to the semitransparentreflecting surface d, which is a suitable light-dividing means adaptedto transmit substantially half of the light and to reflect substantiallyhalf of the light, said surface d being arranged at an angle of 450 tothe path of the beam. The reflected part of the beam, i. e.substantially half of the beam b3, or onethird of the total beam B,passes along path b* to the totally reflecting right-angle prism D whoseapex is in the same horizontal plane as the light beam b4 and at anangle of 45 thereto. This prism D, being centrally located with respectto the horizontal plane of the beam, does not shift the beam butreverses the image and reflects the beam along path b5 and forms animage on the film at N. A plane reflector would accomplish the samepurpose as prism D, except that it would not reverse the image, whichwould then not be arranged similarly to the other two.

The part of the light transmitted by surface d, passes along path be tothe upper right-angle totally reflecting prism E, which is similar toprism C but oppositely arranged and has its apex E above the plane ofthe light beam. The beam 6 strikes theI lower face E2, from which it isreflected along path bl to the upper face E3. This shifts the beamsidewise with relation to the prism, that is, upward and lengthwise ofthe film, and reverses the image. From surface E3 the beam passes alongpath bg to the totally reflecting surface r. which is at an angle of 45Dto the beam. and thence along path b9 to the film F, forming an image atO.

The three images are similarly arranged. or head-to-foot, since eachsplit beam is once reversed by a right-angle prism, and once reflected.The ent-ire apparatus ma)Y be made in the form of a solid block ofglass, of which the prism-surfaces indicated form part of the boundingsurface. The incidence is in all cases so oblique as to insure totalreflection.

A feature in all of the above arrangements is exact equality between thetwo or more optical paths from lens to images. This is attained eitherby complete geometrical symmetry with respect to the surface whichsplits the beam, or (as in the case of the head-tofoot images) by theexact optical equivalent of such symmetry, in that the lengths of thepaths of the split beams in glass and in air are the same. This ishighly advantageous as only in this way can the optical corrections forthe glass be performed all at once by a single correcting device for theentire beam before the beam is split.

An important problem solved in each of the above devices is to obtainthe desired arrangement of images and the necessary equality of paths,without excessive length of path from lens to images. This restrictionresults from the rigid limitation imposed by practical considerations onthe focal length of the lens used,-a limitation which excludes manypossible arrangements because of the too great length of path theyrequire.

It follows that, unless metal reflectors are used (which in general isnot feasible), in systems involving a single lens, a large part of thepath from lens to .images must lie within the glass prisms used todivide and manipulate the light. It is well known in the optical artthat this mass of glass (optically equivalent to a single slab in astraight beam) introduces aberrations tending to impair the gooddefinition of the image. Chief among these are curvature of field,chromatic aberration, and spherical aberration. Means for correctingthese aberrations as fully as the various conditions allow forms no partof the invention herein claimed, and are therefore not described.

In order to eliminate the problem of making such correction separatelyfor each division of t-he beam, and to permit its correct accomplishmentonce for al1 at or near the lens, it is highly desirable that the partof every path from lens to image which lies in glass be made equal; thatis, that each part of the beam, after division, traverses the samedistance in glass. This is an important feature of all the abovearrangements.

It is of great importance that the geometrically identical images beforereferred to should be taken on the same film and not very distant fromeach other; and in practice the ima-ges of each complemental set shouldbe adjacent, the practical limit of separation being of the order ofmagnitude of the width of the film. There are several reasons for this,In the first place, any lm, during the mechanical and chemical processesof developing and fixing, undergoes a certain amount of change in form,principally shrinkage, and in general it cannot be assumed that twoseparate films will shrink to the same degree. Therefore, if the imageswere taken on two or more different films, they could not be relied uponto remain accurately the same in size through the process ofdevelopment, printing and projecting upon the screen.

In the second place, the accurate superposition of two or more pictureson the projecting screen depends on the two or more images on the filmused in projection, being either positioned to extreme accuracy or outof position by the same small amount. Actual practice proves that lackof register on the screen is more annoying than an irregulardisplacement of the picture as a whole, that is, of all of the two ormore superimposed images to the same degree. It is therefore importantthat the relative position on the screen of the two or moregeometrically identical images should be more accurately constant thanthe mere positioning of non-attached films by the mechanism of theprojector can accomplish. When the two or more images are on the samefilm and the film is treated uniformly throughout its length, pictureson the projecting screen once in register will remain accurately inregister, since the slight irregularities of the mechanism when thepictures are similarly oriented involves similar displacements for allof the superimposed screen images.

From the foregoing description it is evident that the present inventioninvolves among others the following unique features: The variousreflecting and semi-reflecting surfaces are so inclined with respect toeach other and to the incident beams that the angles subtended by theincident and reflected beams are oblique, i. e., either acute or obtuse,rather than right angles. The surface through which the main beam fromthe object field enters (0M-wz in Fig. l and m2 in Fig. 2, e. g.) isutilized as a reliecting surface to reflect one of the divided beams.The images are formed in non-super- U-l annum posed relationship and infiatwise alinement, i. e., in the same plane, and the plane of theimages is angularly disposed with respect to the plane of thelight-dividing surfaces, i. e., the two planes are not parallel. And theimage plane is oblique to the axis of the main beam B.

The images are formed in parallel relationship or with correspondingrectilinear lines in parallelism. For example if a vertical pole or ahorizontal cable appears in the scene, the pole or cable in each imageof a complemental set is parallel to the corresponding element in eachof the other complemental images of the set, although the correspondingelements may be reversed, that is, have their heads or othercorresponding sides directed in opposite directions, in respectiveimages of each set. The paths of the main beam and the paths of thedivided beams lie in the same plane, for example the plane ofthe paperin Figs. 1 and 2.

Each of these characteristics contributes to the aforesaid objects andresults attained by the present invention, particularly to the desiredarrangement of images and the necessary equality of paths withoutexcessive lengths of paths, and while all of these characteristics arecombined in the illustrated embodiments of my invention they may beutilized independently or in sub-groups within the scope of the appendedclaims.

I claim: l

l. A system for producing a plurality of images of an object field fromthe same point of view at the same time on the same side of a film,comprising means including a transmitting-reflecting surface fordividing a. beam of light into a plurality of similar beams and meansfor reiiecting the divided beams to adjacent picture spaces on the film,the paths of the divided beams being substantially equal in length andsaid surface being inclined to reflect at an oblique angle.

2. A photographic apparatus for producing from a single point of viewtwo images separated from each other in the same plane comprising areflecting prism unit having a plane incident beam receiving face andemergent beam faces in a single plane at an angle to the axis of theincident beam, a light dividing refiector at another surface of the unitand certain surfaces of the unit extending across the paths of thedivided beams at total reflecting angles to form images separate fromone another along the focal plane.

3. A photographic apparatus for producing from a single point of viewtwo images separated from each other in the same plane comprising areiecting prism unit having a plane incident beam receiving face andemergent beam faces in a single plane at an angle to the plane of thelncident beam receiving face, a light dividing reector at anothersurface of the unit and certain surfaces of the unit extending acrossthe paths of the divided beams at total reflecting angles to form imagesseparate from one another along the focal plane, said surfaces being soinclined to the respective beams that the angles subtended by theincident and reflected beams are oblique.

4. A photographic apparatus for producing from a single point of viewtwo images separated from each other in the same plane comprising areflecting prism unit having a plane incident beam receiving face andemergent beam faces in a single plane at an angle to the p-lane of theincident beam receiving face, a light dividing reflector at anothersurface of the unit and certain surfaces of the unit extending acrossthe paths of the divided beams at total reflecting angles to form imagesseparate from one another along the focal plane, said reflector and saidsurfaces being so inclined to the respective beams that the anglessubtended by the incident and reflected beams are oblique.

5. A photographic apparatus for producing from a single point of viewtwo images separated from each other in the same plane comprising areflecting prism unit having a plane incident beam receiving face andemergent beam faces in a single plane at an angle to the plane of theincident beam receiving face, a light dividing reflector at anothersurface of the unit and certain surfaces of the unit extending acrossthe paths of the divided beams, at total reflecting angles to formimages separate from one another along the focal plane, said surfacesbeing so inclined to the respective beams that the angles subtendedbetween the incident and reflected beams are obtuse.

6. A photographic apparatus for producing from a single point of viewtwo images separated from each other in the same plane comprising areflecting prism unit having a plane incident beam receiving face andemergent beam faces in a single plane at an angle to the plane of theincident beam receiving face, a light dividing reflector at anothersurface of the unit and certain surfaces of the unit extending acrossthe paths of the divided beams, at total reflecting angles to formimages separate from one another along the focal plane, said reflectorbeing so inclined to the respective beams that the angle subtendedbetween the incident and reflected beam is acute and said surfaces beingso inclined to the respective beams that the angles subtended betweenthe incident and reflected beams are obtuse.

7. A system for simultaneously producing on the same side of a film aplurality7 of similar images of an object field which comprises a partlytransmitting and partly refleeting surface for dividing a beam of lightinto a plurality of beams and reflecting surfaces for reflecting thedivided beams to the film, said first surface being so inclined that theangle subtended between the incident and reflected beams is acute.

8. An optical system for color photography comprising a plurality ofreflecting surfaces correlated to direct parts of a beam of light toseparate spaces on the same side of the film, one of the surfaces beinga partially transmitting and partially reflecting surface in opticalalinement with another of the surfaces, both of the surfaces beinginclined in the same direction but at diderent angles relatively to thepath of the light passing through the first of said surfaces.

9. A system for simultaneously producing on the same side of a film aplurality of similar images of an object field which comprises a partlytransmitting and partly refiecting surface for dividing a beam of lightinto a plurality of beams and reflecting surfaces for reflecting thedivided beams to the film, said first surface being so inclined that theangle subtended between the incident and reflected beams is acute andcertain of said last surfaces being so inclined that the anglessubtended between the incident and reflected beams are obtuse.

l0. In a system for simultaneously producing on the same side of a filmcomplemental images of an object field from the same point of View, thecombination of focusing means and prism means, the prism means includinga light-dividing surface and surfaces arranged to bend the divided beamsin such manner th'at the complemental images produced thereby areangularly but symmetrically disposed with respect to the plane of thelight-dividing surface and in parallel relation to each other.

l1. A system for producing complemental images of an object fieldcomprising a lightdividing surface and reflecting surfaces arranged toposition the complemental images in spaces in the same plane which areangularly disposed with respect to the plane of the light-dividingsurface and which are disposed on opposite sides of said planeequidistantly therefrom with certain of their margins parallel thereto.

l2. A system for producing complemental images of an object fieldcomprising a light-dividing surface and reflecting surfaces arranged toposition the complemental images in spaces which are substantiallyperpendicular to the plane of the light-dividing surfaces and which areequidistant from said plane on opposite sides thereof and which havecerta-in of their margins perpendicular thereto.

13. A system for producing complemental images of an object fieldcomprising a lightdividing surface and reflecting surfaces arlli) rangedto position the complemental images in spaces which are substantiallyperpendicular t0 the plane of the light-dividing surface, and which aresubstantially in fiatwise alinement and which are equidistant from saidplane on opposite sides thereof, and which have juxtaposed marginsparallel to said plane.

14. In a system for simultaneously producing on the same side of a filmcomplemental images of an object field from the same point of View, thecombination of focusing means and reflecting means correlated to formthe compleniental images in uxtaposed picture spaces on one side of thefilm in reversed and parallel relationship With respect to each other,said reflecting means comprising a partially transmitting and partiallyreflecting surface disposed at an angle to the plane of said picturespaces.

15. In a system for simultaneously producing on the same side of a filmcomplemental images of an object field from the same point of View, thecombination of f0- cusing means and reflecting means comprising areflector disposed in a plane perpendicular to the film, said meansbeing correlated to form the complemental images on the filmequidistantly from said plane, and said reflecting means being arrangedto form the images in a plane making an angle to the axis of thefocusing means.

16. A system for producing complemental images of an object fieldcomprising a lightdividing surface and reflecting surfaces arranged toposition the complemental images in parallelism and substantially inflatwise alinement in spaces which are separated along the length of thefilm and which are disposed equidistantly from the plane of thelight-dividing surface on opposite 'sides thereof.

17. A system for producing complemental images of an object fieldcomprising a light.- dividing surface and reflecting surfaces arrangedto position the complemental images in parallelism and equidistantlyfrom the plane of said light-dividing surface in spaces separated fromeach other along the plane of the film.

18. A system for simultaneously producing a plurality of images of anobject field substantially in the same plane comprising means fordividing the main beam of light from the object field into a pluralityof similar beams, and means for reflecting the divided beams at suchangles as to form the imagesin spaces separated along a plane oblique tothe axis of said main beam at equal distances on opposite sides of theplane of the light dividing means.

19. In a system for simultaneously producing complemental images of anobject field from the same point of View, the combination of focusingmeans, light-dividing means in optical alinement with the focusing meansfor dividing a beam of light into a plurality of parts, the focusingmeans being adapted to cause the divided parts of the beam to produceimages, and reflecting means arranged in the paths of the divided partsof the beam so as to position the images in the same plane withcorresponding sides directed in opposite directions.

20. In a system for simultaneously producing complemental images of anobject lield from the same point of View, the combination of focusingmeans, light-dividing means in optical alinement with the focusing meansfor dividing a beam of light into a plurality of parts, the focusingmeans being adapted to cause the divided parts of the beam to produceimages, and reflecting means arranged in the paths of the divided partsof the beam so as to position the images in the same plane with theirheads directed in opposite directions, the geometrical lengths of saidpaths in similar media being equal.

21. In a system for simultaneously producing on a film complementalimages of an object field from the same point of View, the combinationof focusing means, and prism means, the prism means including alight-dividing surface and reflecting surfaces, the said means beingdisposed in optical alinement in such manner that the complementalimages produced thereby are symmetrically disposed With respect to theplane of the light-dividing surface in separate spaces along one side ofthe film with corresponding lines of the images parallel to each other.

22. In a system for simultaneously producing on a film complementalimages of an object field from the same point of view, the combinationof focusing means, and prism means having a light-dividing surface andreflecting surfaces in optical alinenient with the focusing means, saidsurfaces being arranged to position the images in separate spaces alongthe same side of the film, and the reflecting surfaces beingsymmetrically disposed With respect to the plane of the light-dividingsurface.

23. In a system for simultaneously producing on a film complementalimages of an object field from the same point of view, the combinationof focusing means, and prism means, the prism means having alight-dividing surface and reflecting surfaces in optical alinement withthe focusing means, the reflecting surfaces being arranged to positionthe images transversely of the plane of the light-dividing surface andthe light-dividing surface being so disposed With respect to the path oflight from the object field that the paths of the divided light are smmetrically dis osed with respect to sai plane, all of sai paths lyingin the same plane, whereby complemental images are symmetricallyproduced relatively to said plane.

A system for producing on a film a plurality of images of the sameobject from accurately the same point oi." view at the same time. whichcomprises means for dividing the light beam into two paths including aplane surface which reflects part' of' the light and transmits part ofthe light, and means to refiect the divided parts of the beam alongpaths which are symmetrical with respect to the plane where the light isdivided, said means being arranged to position the images on the film innon-superposed relationship with corresponding lilies of the imagesparallel.

Q5. A system for producing a plurality of images ot' the same objectfrom accurately the same point of view at the same time, comprising apartly transparent reflecting plane adapted to divide the light beaminto two parts, and means to project the two parts of the divided beamin distinct paths symmetrical to said plane with said paths and saidlight beam in the same plane. said means being arranged to position theimages on the film in Spaces which are separate from each other alongthe film.

26. A system for producing a plurality of images of the same object fromaccurately the same point of view at the same time, comprising twoidentical juxtaposed prisms in the path of the light beam from theobject to the image surface, and a partly transparent reflector betweenthe juxtaposed surfaces of said prisms adapted to reflect part of thelight back through the. same prism to the surface through which itentered and to transmit part of the light through the other prism.

27. A. system for producing on a straight film a plurality of images ofthe same object field from accurately the same point of view at the sametime, comprising a lens, and a partly transparent plane between the lensand the film adapted to divide the light into two paths, and reflectorsfor reflecting the divided light to spaces separate from each otheralong one side of the film, margins of said spaces being arranged inparallel juxtaposition and said plane being arranged to intersect thefilm symmetrically between juxtaposed spaces.

28. A. system for producing on a straight film a plurality of images ofthe same object Jfrom accurately the same point of view at the sametime. comprising a lens, a pair of juxtaposed prisms between the lensand film, and a partly transparent reflecting plane between said prisms,adapted to divide the light into two paths, said reflecting plane beingangularly but symmetrically arranged with relation to the image spaces,

and said prisms having reflecting surfaces arranged to reflect the lightto the film.

2i). .t system for producing on a straight film a plurality of images ofthe same object from accurately the same point of view at the same time.comprising a lens, a pair of juxtaposed prisms between the lens andfilm'` and a partly transparent reflecting plane between said prisms andbisecting the angle formed between the outer surfaces of said prismsadapted to divide the light into two paths, said reflecting plane beingangularly but symmetrically arranged with relation to the image spaces,and said prisms having refiecting surfaces arranged to reflect the lightto the film.

30. A system for producing on a film a plurality of' images of the sameobject from accurately the same point of view at the same time,comprising a lens, a pair of identical, juxtaposed prisms between thelens and the film, a cross section of each prism forming a right angletriangle and said two triangles together forming an equilateraltriangle, a partly transparent reflecting plane between said two prismsadapted to divide the light into two paths, said refleeting plane andthe image spaces being symmetrically arranged, and the prism surfacethrough which the light first enters being normal to the light.

3l. A system for producing on a film a plix'ality of images of the sameobject from accurately the same point of view at the same time,comprising a lens, a pair of juxtaposed prisms between the lens andfilm, a partly transparent reflecting plane between said prisms, adaptedto divide the light into two paths, said reflecting plane beingsymmetrically arranged with relation to the image spaces, and anotherpair of similar prisms with a partly transparent reflector betweenthemin the path of one at least of said divided beams, adapted again todivide said divided beam into two paths.

32. A system for producing on a film a plurality of images of the sameobject from accurately the same point of view at the same time,comprising a lens, a pair of juxtaposed prisms between the lens andfilm, a partly transparent reflecting plane between said prisms, adaptedto divide the light into two paths, said reflecting plane beingangularly but symmetrically arranged with relation to the image spaces,and means in the path of one of said divided beams adapted optically toinvert the image.

33. In a photographic apparatus in which the incident rays are dividedand the divided emergent rays are parallel and separated from each otherto simultaneously form two images of the same object displaced from eachother in the same plane and adapted to be superposed in congruentrelation, an image forming optical train embodying an objective, a lightdividing device and reflectors set at angles to direct the dividedemergent rays parallel and laterally displaced with relation to eachother but with their axes at an obtuse angle to the axis of the incidentrays, the light paths of the two divisions being equal in length andhaving a common focal plane.

34. In a system for simultaneously producing on the same side of a filmcomplemental images of an object field from the same point of View, thecombination of focusing means and prism means, the prism means includinga light-dividing surface for dividing a main beam into similar dividedbeams and surfaces arranged to bend the divided beams in such mannerthat the complemental images produced thereby are angularly butsymmetrically disposed with respect to the plane of the light-dividingsurface, said surfaces being angularly arranged with respect to the axisof the main bea-m to produce the images in a plane which intersects theaxis of the main beam.

35. In a system for simultaneously producing on the same side of a filmcomplemental images of an object field from the marismas same point ofView, the combination of focusing means and prism means, the prism meansincluding a light-diyiding surface for dividing a main beam into similardivided beams and surfaces arranged to bend the divided beams in suchmanner that the complemental images produced thereby are angularly butsymmetrically disposed with respect to the plane of the light-dividingsurface and in alinement on the iilm with their sides in juxtapositionthroughout the Width thereof.

36. In a system for simultaneously producing on a film complementalimages of an object field from the same point of view, the combinationof focusing means, and prism means having a light-dividing surface andreiiecting surfaces in optical alinement With the focusing means, saidsurfaces being arranged to position the images in separate spaces alongthe same side of the film, and the reiiecting surfaces beingsymmetrically disposed with respect to the plane of the light-dividingsurface and having rectilinear elements arallel to said plane.

Signed by me at oston, Massachusetts, this 28th day of January 1916.

DANIEL F. COMSTOCK.

